Progress towards Understanding the Charge Transport Hopping Mechanism in Molecularly Doped Polymers

Abstract

Recent progress towards understanding the charge transport mechanism in molecularly doped polymers MDP is reviewed. It has already been shown that the mobility is not understandable in terms of the Gaussian Disorder Model (GDM) or any other available model. In this paper, it is shown that characteristic features of the current-time transient are also not understandable in terms of available models. In addition, a method has been used to convert disorder energies obtained from GDM into Arrhenius activation energies. Using this methodology a list has been compiled of the activation energies of all molecularly doped polymers which have been characterized as a function of dopant concentration. This list demonstrates that disorder and polaron binding energies are small compared to observed activation energies, suggesting that some higher energy process determines the charge transport mechanism in MDP. The experimental observations of activation energies that depend on ρ, the distance between hoping sites, and pre-factors independent of ρ are attributed to either interactions among the dopant molecules or the failure of the lattice gas model to properly calculate ρ at high dopant concentrations.